Output control for hot air gas turbine plant



p 7 9 .c. GREY 2,806,684

OUTPUT CONTROL FOR HOT AIR GAS TURBINE PLANT 4 Sheets-Sheet 1 FiledApril 30, 1956 Fmal so v I I I lo so 40 so so 90, I00 no :20 I30 no I50Inventor ymmm,m

A, Aftornrysv4 S heets-Sheet 2 .PTM

J. C. GREY ou'rP u'r doNTR L. FOR 501 AIR GAS TURBINE PLANT Filed Aprilso, 195

Sept17, 1957 J. c. GREY v v om urfcomomoa nor AIR GAS TURBIJNE PLANTFiled April so; 1956 l 4 Sheets-Sheet s v .I A

. voLuma SELECTOR PRESSURE Sucronpv lnven'l'or Sept 17; 1957 J. c. GREYYv OUTPUT CONTROL FOR HOT AIR GAS TURBINE PLANT Filed April so; 1956 4Shasta-Sheet 4 WWW ' ATTORNEYS ,.U/ M ,mm 1 M o R n M 1 4 O 1 M J f m Ho N m. m E s c E F W W m m Unite States OUTPUT CONTROL FDRHOT AIR GASTURBINE PLANT John Constantine Grey, Isleworth, England, assignor toPower Jets (Research & Development) Limited, London, England, a Britishcompany Application April .30, 1956, Serial No. 581,652 Claims priority,application Great Britain June 1, 1951 12 Claims. (Cl. 26319) furnace;first, because resistance to air flow is produced by a mass of porousmaterial, and second, the aerodynamic properties cannot be accuratelypredicted. Thus, whereas at a given instant it may be broadly true thatan increase in volume requires an increase in pressure, their numericalrelationship may vary from day to day, according to the state of thefurnace charge. The actual required values of the pressure, volume andtemperature are dictated by experience and the engineer in charge needscontrol over each one, independently of the other two.

While aiming at as much measure of independence as possible, it is clearthat of the three variables, only the temperature can be reallyindependent, whereas the pressure and volume are related to each otherby the blast furnace characteristics. Thus operation at constantpressure involves large variations of volume flow and, conversely,operation at constant volume (or mass flow) necessitates considerablevariation in blast pressure.

An object of the invention is to provide control of the blast air supplyto a blast furnace either for constant pressure or constant mass flowconditions, which control is automatically effected in normal operation,over-riding manual supervision being able to be introduced without delayfor controlling abnormal operations.

It has previously been proposed to provide the blast air supply from agas turbine plant. Moreover it has also been suggested that an easilyadjustable arrangement will comprise an open cycle single-shaft plantwith two turbines one of which has a throttled stream of working fluidand which gives supplementary power to maintain the plant self-driving.In one such plant a by-pass duct leads a portion only of the main airstream to be expanded in the throttled turbine. Another part of thestream forms the blast supply. More than one cycle arrangement of thisnature is possible. In one described below division of the air streamfollows after it has been passed wholly through one of the turbines. Inanother cycle the air stream is split immediately downstream of thecompressor, neither turbine receiving the whole stream. Reheatingarrangements before the throttled turbine are preferably incorporated.

It is proposed to unite together gas turbine blast furnace air supplyplant with an arrangement for effecting the desired control mentionedabove.

Patented Sept. 17, 1957 'ice means for controlling the air pressure atthe delivery point of the compression stage of the plant in accordancewith the mass flow of air supplied to the furnace and with the blastair-supply pressure acquired by the furnace.

The control arrangement may be operated so as to provide in normaloperation a .blast air supply either of constant mass flow or atconstant pressure. Preferably the control is effected via a throttlefitted in the lowpressure outlet duct of'an auxiliary turbineincorporated for the reasons specified above. In this case variation inwork done by the auxiliary turbine adjusts the compressor deliverypressure. The control arrangement may comprise mechanicalservo-mechanisms. Alternatively, electrical remote control'may beemployed.

The invention also provides a control arrangement for a gas turbineblastfurnace blower plant which plant comprises a rotary air compressor, twoturbines each provid ing' drivin'g torque for the compressor with a partonly of the air stream through the plant being expanded through one oftheturbines, another part being delivered as the blast supply and heatinput means, the control arrangement comprising means for varying thepower outputof said one turbine thereby varying the delivery pressure ofthe compressor and differential means automatically responsive to themonitored compressor delivery pressure, to the monitored air mass flowsupplied to the furnace and to a predetermined setting of blast pressurerequired to control the power varying means.

"lhe invention will nowbe described with reference to one embodimentthereof shown in the accompanying drawings in which:

Figures 1, 2 and 3 are graphs showing the operating characteristics ofgas turbine air blower equipment in relation to an associated blastfurnace.

Figure 4 is a general schematic diagram of an arrangement forming theembodiment of the invention to be described.

Figure 5 is a more detailed view of the mechanical differential controloutlined in Figure 4.

Figure dis a side view of a cam seen in Figure 5.

Figure 7 is a detailed view of the control box which is shownschematically in Figure S.

Figure 8 is a detailed view of the mass flow monitoring equipment shownschematically in Figure 5.

Figure 9 is a schematic of an alternative electrically operated controlcircuit.

The required operating characteristics of a control arrangementaccording to the invention will be appreciated by reference to Figuresl-3.

References used in the following argument are as follows:

PT=Main turbine inlet pressure t'r=--Main turbine inlet temperature PbBlast pressure M=Airmass flow to blast furnace t =Blast temperatureFigures 1 and 2 show the characteristics of the air turbirre blower, i,e. the main turbine inlet pressure (which is approximately the same asthe compressor delivery pressure in the arrangement of Figure 4described below and is here plotted as such) and temperaturerespectively that are required in order to sustain given blast pressuresand mass flows. (The mass flow is shown as percent of maximum continuousflow at the blast pressure of 20 p. s. i. g.) Thus, if the blast furnacewill accept M =70% at Pb=10 p. s. i. g., the turbine inlet conditionshave to be P ==68 p. s. i. .g. and t =55O C. as denoted by points AandA; In Figures 1 and 2 respectively, an increase l l l of mass flow atconstant 'blast pressure requires an increase of turbine pressure asshown in Figure 1 but constant turbine temperature is maintained asFigure 2 shows. The changes are indicated by arrows (a). In anothercase, an increase of blast pressure at constant mass flow requires anincrease of both turbine pressure and temperature as indicated by arrows(b) in the two figures. In practice, an increase of blast pressure wouldprobably be accompanied by some increase of mass flow as indicated byarrows (c). The linear blast pressure/mass flow relationship is shown inFigure 3.

Assuming that the turbine is delivering steadily at the operating pointA, any deliberate departure from this point, say an increase of massflow and/ or blast pressure, must be initiated by an increase in turbinespeed. In the arrangement of Figure 4, this may theoretically beobtained either by an increase in turbine inlet temperature or by inincrease in power output from the auxiliary turbine. The latter methodis adopted because of the slow response to attempts to adjust turbinetemperature.

The general layout of the blast air supply plant will be appreciatedfrom Figure 4. In this control apparatus and connections are shown inheavy print. The cycle diagram is drawn more faintly. The turbine plantconsists of an air compressor CP, a main air turbine MT and an auxiliaryair turbine AT, all mounted on the same shaft. There are indirectheaters AH and BH, the former being primarily the turbine heater and thelatter the blast heater. It will be seen that some of the output streamfrom the main turbine MT after passing through the blast heater 81-1 isby-passed to provide working fluid for expansion in the auxiliaryturbine AT. The main airstream is taken direct to the blast furnaceshown at BF. In the outlet duct of the auxiliary turbine there is athrottle T by means of which the power delivered to the shaft by thisturbine may be adjusted.

There are two main control arrangements associated with the plant, oneof which i the temperature control of the air heaters and therefore alsoof the inlet air to the main turbine and of the blast air. This isexercised by the adjustment of the combustion regulator P, by means ofwhich the quantity of fuel burned in the air heater may be adjusted inknown manner. The heaters AH and EH are fired in the same way as gasfired boilers; they are blown by electrically driven fan and theircontrol does not involve any new problems and so forms no new part ofthe invention. The control of the blast temperature is entirelyindependent of the operation of the air supply plant and may be selectedin advance and varied as required. The other control arrangement, towhich the invention particularly relates, is concerned with theregulation of a gas turbine air blower equipment. In one form itcomprises a mechanical arrangement as indicated in Figure 4 to 7. A massflow monitor FM is inserted in the blast airstream being delivered tothe furnace and its reactions are communicated to the control box 51.Mass flow monitors are themselves known and the most accurate kind arethose which comprise a venturi restriction in the duct with means formeasuring venturi head, absolute pressure and temperature. Thesemeasurements may be combined to give a movement of a control lever whichis a close approximation to changes in the actual flow valve. In Figures4 and 5 the flow monitor FM has been diagrammatically shown, and thedotted line between the monitor and the control box S1 represents thetransmission of a shaft movement directly proportional to mass flow. InFigure 8 is represented a known type of flow monitor which indicates themass flow through a venturi in a duct D at any moment by the position ofa link L. The volume flow through the venturi V depends upon thedifference in pressure upstream and downstream of the venturi. Theseupstream and downstream pressures are effective through pipes P1 and P2respectively, and act on the inner and outer surfaces respectively of abell BL partially submerged .in a liquid as shown. A pressure actingwithin the bell sutficiently greater than that acting without, willcause the bell to rise, and the lever R and steadying link LS to moveabout their pivots. This causes a downward movement of the vertical rodRV, which is translated to a horizontal movement of the link L by meansof a bell-crank BC. The bell BL is constructed and shaped in such amanner that its movement, and consequently that of the link L, ilinearly related to the rate of flow in the duct D. Compensation fordifferent temperature and pressure conditions within the flow is made byvarying the effective length of the lever R between its pivot and itspoint of attachment to the rod RV, a slot beingprovided in the lever Rfor this purpose. Variation in the position of the rod RV along the slotwill therefore influence movement of the link L, and thi variation ismade dependent upon variations of pressure and temperature within theduct by means of Bourdon tubes p and t respective-1y, connected to theduct D downstream of the venturi V by means of pipes P4 and P3. Suchvariations in pressure and temperature will cause movement of the freeends of the tubes 2 and t, and of the floating beam FB attached thereto.Any horizontal movement of the central point of the beam FE a shown willdepend upon the combined effect of temperature and pressure, and will beconveyed by the rod RX, lever LX and rod RY to the upper end of the rodRV, thus controlling the movement of the rod RV in the slotted end oflever R, and influencing the movement of the link L as described. Theaction of the link L is conveyed to the control box S1, and may besupplemented by a conventional servo mechanism if required. This controlbox S1, which is more fully described in Figure 7, adjusts a cam PVCwhose follower is connected to the differential control C. This controlis also responsive to the main turbine inlet pressure, an air connectionbeing taken from the inlet duct for this purpose. The differentialcontrol acts via mechanical transmission and a servo-motor S2 toregulate the throttle T in the downstream duct of the auxiliary turbineAT.

The control arrangement outlined above may be more fully seen in Figures5 to 7 and the actual operation of the plant will be described fromthese figures. Referring first to Figure 5, it will be'noticed thatthere are two handwheels for manual adjustment of the controlarrangement, one is for selection of mass flow or volume of the blastair supply and the other i a blast air pressure selector. The volumeselection handwheel is connected to the control box S1 and that in turnmoves a rack RE. The internal arrangement of the control box isindicated in Figure 7.

The link L in Figure 7 transmits to the control box the mass flowmonitors indications. The movements are transferred to one end of aswinging link reversing mechanism RM the purpose of which will beapparent later. The swinging link itself SL has a handle RL on it whichextends outside of the box and enables reversal to be accomplished. Themovement of the link L is transmitted directly, or in reverse as thecase may be, to the guided rod FL. To the end of the rod FL there isfitted a piston FF which is a friction fit in the cylinder FC. Normallythe movements of FL, following those of the link L, are directly passedon to the rack RE which is connected to the cylinder FC. To the side ofthe cylinder FC is attached a rack VR which is engageable by the pinionVP on the shaft of the volume selection handwheel. The relativepositions of the cylinder FC and the piston F? can therefore be adjustedby manual operation of the handwheel overcoming the friction drive.According to the handwhecl operation so is the rack first positioned;thereafter that rack follows the mass flow monitors responses. In thedescription of the operation of the control arrangement, it will beassumed that the engineer in charge of the blast furnace has beenordered to maintain a constant blast pressure. The action needing to betaken is discussed below.

Reference to the curves of Figures 1 and 2 shows that the mass flow maybe varied widely at any given blast pressure providing that the turbinetemperature follows the appropriate line in Figure 2 and the turbineinlet pressure and compressor delivery pressure follow the appropriateline in Figure 1. Thus, at a blast pressure of p. s. i. g. in order toincrease the mass flow from 70% (point A) to 100% (point B), the turbinetemperature must remain substantially constant but the turbine pressuremust be increased from 68 p. s. i. a. to 87 p. s. i. a., i. e. theturbine speed must be raised.

The increase of speed from vA to B can only be obtained by increasingthe turbine power during the transition from A m3, and in the absence ofother means, this would normally be achieved by a temporary increase inturbine temperature so that the operating point would travel in thedirection of arrow (0) before settling on point B. The disadvantage ofthis method is that, due to the thermal inertia of the air heater AH,the increase in turbine temperature is a relatively slow operation (aquestion of minutes) and the control here provided over the throttlevalve T downstream of the auxiliary turbine provides a considerablespeeding up ofadjustment. This auxiliary turbine is normally designed tooperate against a pressure somewhat above atmospheric so that, when anacceleration is required from the unit, it may be obtained atpractically constant turbine temperature simply by opening throttle T,thereby increasing the work output of the auxiliary turbine. Under thesecircumstances, the rapidity of response is almost instantaneous (aquestion of seconds). It should be noted that the opening of throttle Tis of a transient character so that when the operating point reaches B,the valve T will be closed slightly in order to restore to the auxiliaryturbine approximately its original pressure ratio, i. e. the pressureratio when operation was at point A.

Assuming now that the control gear has been manually adjusted so thatPb=10 p. s. i. g., the rack RA having been positioned correspondingly asa result. Assume also that a mass flow has been obtained giving tr=550C. in accordance with Figure 2. These handwheel movements effect bothaxial and angular motion of the cam PVC. The pressure selecting wheelrotates a pinion on a rack RA which is integral with the shaft CS onwhich the cam is mounted. Hence longitudinal movement is imparted to thecam with a result on its follower CF which can best be seen from the camside View, Figure 6. The mass flow or volume selecting handwheel movesthe rack RB with which a pinion fixed to shaft CS engages. This pinionis, of course, of sufficient width to accommodate longitudinal movementsof shaft CS without disengagement from the rack RB. Hence angular motionof the cam PVC is obtained. It will be recalled that rotation of PVC isalso obtainable by driving the rack RB directly from the mass flowmonitor FM.

The cam follower CF is extended to form part of the differential controlC. The latter consists essentially of a spring-extended capsule orbellows within a sealed casing. The spring is normally compressed andadditional spring force is exerted whenever the cam follower rides up.The skirt of the bellows is attached to the casing and the outside ofthe bellows is subject to the pressure PT communicated via theconnection from the turbine inlet.

The spring pressure exerted in the differential control depends on theposition of the cam follower CF. The profile of PVC is therefore soshaped that for any given mass flow the spring pressure balances theappropriate P1 in accordance with Figure 1. Thus a steady condition suchas has been assumed results in the extension of the bellows remainingconstant. Lack of balance causes the bellows to expand or contract andthe bellows follower F, which has a limited travel, is raised orlowered. This movement is communicated to the servo-motor S2 which inturn regulates the auxiliary turbine throttle T,

6 openingit when F moves upwards and shuttingit when F moves downwards.

With this interaction of parts it follows that clockwise rotation andmovement axially to the right (as seen in Figure 6) of PVC lowers thecam follower CF. Hence the spring pressure .in the differential controlis reduced, the bellows are compressed by the air pressure PT, thefollower F .drops and S2 closes the throttle T. This causes the .powerdeveloped by the auxiliary turbine to be decreased and the shaft speedfalls. The compression ratio of the compressor CP (Figure 4) is loweredand at a new smaller valueof PT equilibrium is again established in thedifferential control, the throttle T condition "beingautomaticallyreadjusted to a new position.

Anticlockwise rotation and/ or movement axially to the left (as seen inFigure 6) of PVC raises CF. By a similar chain of causation a newincreased balancing value of PT is obtained and a new higher shaft speedobtained.

All these parts are brought into play during a manual operation of thecontrol arrangement. Automatic adjustment is provided for by theintroduction of the control box'Sl which is responsive to the mass flowmonitoring unit, diagrammatically indicated at FM. If the mass flowchanges, the control box Si moves the rack RB correspondingly and sorotates PVC. The direction of rotation is made dependent on Whetherconstant pressure or constantvolume Working is required. In the formercase, which has been assumed above, a reduction in flow is caused toeffect clockwise rotation of PVC and vice versa. Hence, ifthe mass flowthrough the blast furnace diminishes, say, due toa stiffening charge inthe furnace, the controlibox S1 will rotate the cam clockwise until theturbine inlet pressure is lowered and equilibrium is restored.

In order to achieve automatic constant volume working the onlyv changethat has to be made to the equip- 'ment is that a reduction'in flow noweffects anticlockwise rotation of PVC. This isachieved by reversing theswinging link SL by means of the handle RL.

For example, assume that the plant is operating steadily at point A (seeFigures 1 and 2) and that, as a result of a stiifening charge in theblast furnace, the mass flow diminishes (incidentally with a slighttransient increase in blast pressure). Under the response of the massflow sensitive control box S1, the cam PVC will be rotatedanticlockwise. This produces a higher turbine inlet pressure and in themanner described above. In Figure l the operation can be seen first as amass flow reduction, arrow a, and then as an increase of PT andrestoration of M, arrow e. This process will go on tending to restorethe original equilibrium position. Failure to do so completely is anindication to the operatorthat the selected blast pressure is too low toachieve the desired mass flow. He then selects a progressively higherblast pressure until the mass flow indicator reading is restored.

v The mechanical control arrangement shown in Figures 4 to 7 may bereplacedby anequivalent electrical controlling circuit. Such a circuitis shown schematically in Figure 9. A five-position switch BPS, inaccordance with its positioning, taps off a corresponding potentialdifference from the potentiometer PR. This voltage is a measure of theblast pressure setting required and it is furtheradjustable by thepotentiometer MS to a final value dependent also on the mass flowsetting required. The supply, voltage thus developed provides currentvia a rheostat MC and a change-over-switch PVS through one side of adifierential relay DR. The balancing current through the other side ofthe relay DR is developed from a pressure sensitive supply PTM,monitoring the turbine inlet pressure. In equilibrium conditions thesebalance and the relay movable arm makes contact with neither of thefixed stops 1 or 2. If, however, the relay is unbalanced one or other ofthese contacts is made and a circuit is completed to the control TC forthe throttle T, either opening or shutting thelatter.

The operation of the electrical circuit is exactly equivalent to themechanical control already described. The higher the blast pressuresetting the greater the current that flows through the left hand windingof relay DR; to restore equilibrium greater current has also to flowthrough the right hand winding, this follows from an increase in PTbrought about by operation of TC to open the throttle. Larger or smallercurrents in the controlling (left hand) winding are obtained byvariation of the potentiometer MS in response to manual adjustments ofmass flow.

The automatic control, as before, follows the indications of the flowmonitor FM, which is arranged to position the rheostat MC accordingly,thereby altering the controlling current. As shown in Figure 6 assumingthat reduction in mass flow causes the sliding contact of MC to move tothe right, the circuit is arranged for constant volume working. Changeover of the switch PVS automatically alters the control arrangement forconstant pressure working.

Although in the above description the throttle T has been positioned onthe downstream side of the auxiliary turbine AT, which positioning ispreferred, it is possible for it to be situated upstream of AT, as shownat T in Figure 5.

Although over-riding controls have not been shown in the drawings it isintended that they should be incorporated. These controls automaticallyensure that ceiling turbine temperature and speed are not exceeded.There is also included automatic antisurge gear which operates acrossthe intake and delivery of the compressor so that at any given speed itis impossible to reduce the compressor mass flow below the surge limit.The plant incorporates overspeed and overheat controls set to trip theunit to a standstill in the event of either the speed or temperaturesreaching a predetermined value beyond the limit set by the over-ridingcontrols. The stopping of the unit is justified by the possibility of amajor breakdown that would result by the continued operation under suchconditions.

By manually overriding the automatic operation of the control box S1 inthe mechanical arrangement and fixing MC in a home position in theelectrical arrangement the control becomes fully responsive to manualadjustment. Such a return to hand operation is easily and quicklyperformed.

An automatic control system has been described which is capable, bymeans of simple operations, of maintaining the supply of blast aireither at constant pressure with varying mass flow or at constant massflow at varying pressure. The arrangement is such that changes of loadare effected rapidly, the response being independent of the thermalcapacity of the air heaters.

What I claim is:

l. A control arrangement for a gas turbine blast furnace blower planthaving means for compressing, heating and delivering an air supply intoa duct leading to a last furnace, which arrangement comprisesdifferential means responsive on one hand to the air pressure de velopedby said compression means and on the other hand to air mass flow in saidduct, means operable to adjust the pressure ratio of said aircompression means and a connection between said differential means andsaid pressure ratio adjusting means enabling said pressure ratio to bealtered in accordance with the relationship between said air pressureand said mass flow.

2. A control arrangement for a gas turbine blast furnace blower planthaving means for compressing, heating and delivering an air supply intoa duct leading to a blast furnace, which arrangement comprises means forpositioning a device in accordance with air mass flow in said duct,means for altering the effect of said positioning in accordance withmanual adjustment of desired pressure for said blast air supply, furthermeans for altering the effect of said positioning in accordance with amanual adjustment of desired air mass flow in said duct, differentialmeans responsive on the one hand to the eifect of positioning saiddevice and on the other hand to the air pressure developed by saidcompression means, means operable to adjust the pressure ratio of saidair compression means and a connection between said differential meansand said pressure ratio adjusting means enabling said pressure ratio tobe altered in accordance with the relationship between the effect ofpositioning said device and said air pressure.

3. A control arrangement for a gas turbine blast furnace blower planthaving turbine-driven compressing means and indirect heating means foran air supply delivered into a duct leading to a blast furnacecomprising means for adjusting the turbine power input to saidcompression means independently of any adjustment of said indirectheating means a mechanism whose motion is responsive to air mass flow insaid duct equipment for producing pressures corresponding to said motionand differential pressure means operable to control said adjustmentmeans in accordance with the state of balance between said motionrepresentative pressure and turbine inlet pressure communicated thereto.

4. A control arrangement for a gas turbine blast furnace blower planthaving rotary air compression means, a main turbine and an auxiliaryturbine, together driving said compression means, indirect heating meansfor an air supply compressed by said compression means and a ductleading to said blast furnace into which is delivered at least part ofsaid air supply, the arrangement comprising a throttle for the flow ofworking fluid through said auxiliary turbine, means for deriving a firstresponse indicative by its magnitude of outlet pressure from saidcompression means, means for deriving a second response whose magnitudeis based upon the air mass flow in said duct, means for comparing saidfirst and second responses and controlling said throttle in accordancewith the difference therebetween.

5. A control arrangement as claimed in claim 4 further comprising meansfor manual adjustment of the magnitude of said second response incorrespondence with desired air mass flow in said duct.

6. A control arrangement as claimed in claim 4 further comprising meansfor manual adjustment of the magnitude of said second response incorrespondence with desired air pressure in said duct.

7. A control arrangement as claimed in claim 4 in which said secondresponse derivation means incorporates a three dimensional cam and afollower thereof whose movement is transmitted to said comparison andcontrolling means.

8. A control arrangement as claimed in'claim 7 in which said comparisonand controlling means comprises a spring loaded diaphragm whoseextension depends upon transmitted movement of said follower and aconnection through which air pressure constituting said first responseis communicated to said diaphragm to oppose extension thereof.

9. A control arrangement as claimed in claim 4 in which both of saidresponse derivation means produce electrical current responses and inwhich said comparison and controlling means comprises a differentialelectrical relay.

10. A control arrangement for a gas turbine blast furnace blower planthaving rotary air compression means, a main turbine and an auxiliaryturbine, together driving said compression means, indirect heating meansfor an air supply compressed by said compression means and a ductleading to said blast furnace into which is delivered at least part ofsaid air supply, the arrangement comprising a throttle for the flow ofworking fluid through said auxiliary turbine, a three dimensional cam, amanually adjustable mechanism for positioning said cam in one directionof motion thereof, another manually adjustable mechanism for positioningsaid cam in a second direction of motion at right angles to said onedirection, automatic adjustment means for positioning said cam in saidsecond direction in accordance with measurements of air mass flow insaid duct, a differential pressure device, a connection conveying mainturbine inlet air pressure to one side of said device, a follower onsaid cam, means for producing a pressure in said device proportional tomovement of said follower and opposing said turbine inlet pressure and aconnection between said device and said throttle so that the pressurebalance state in the former controls the latter.

11. A control arrangement as claimed in claim 10 in which said throttleis positioned downstream thereof in the direction of flow of its workingfluid.

10 12. A control arrangement as claimed in claim 10 further comprisingmeans for reversing said automatic adjustment means so that the samechanges in said air mass flow may have positioning eflFect upon said camin opposite senses.

References Cited in the file of this patent UNITED STATES PATENTS2,253,809 Pfenninger Aug. 26, 1941 FOREIGN PATENTS 531,997 Great BritainJan. 15, 1941 724,742 Germany Sept. 5, 1942

